Stabilize std::path

This commit stabilizes essentially all of the new `std::path` API. The
API itself is changed in a couple of ways (which brings it in closer
alignment with the RFC):

* `.` components are now normalized away, unless they appear at the
  start of a path. This in turn effects the semantics of e.g. asking for
  the file name of `foo/` or `foo/.`, both of which yield `Some("foo")`
  now. This semantics is what the original RFC specified, and is also
  desirable given early experience rolling out the new API.

* The `parent` function now succeeds if, and only if, the path has at
  least one non-root/prefix component. This change affects `pop` as
  well.

* The `Prefix` component now involves a separate `PrefixComponent`
  struct, to better allow for keeping both parsed and unparsed prefix data.

In addition, the `old_path` module is now deprecated.

Closes #23264

[breaking-change]

1 files changed, 4 insertions, 0 deletions

diff --git a/src/librustc/plugin/load.rs b/src/librustc/plugin/load.rs
index 8267b79ff9e..6fd74479f75 100644
--- a/src/librustc/plugin/load.rs
+++ b/src/librustc/plugin/load.rs
@@ -18,7 +18,10 @@ use std::borrow::ToOwned;
 use std::dynamic_lib::DynamicLibrary;
 use std::env;
 use std::mem;
+
+#[allow(deprecated)]
 use std::old_path;
+
 use std::path::PathBuf;
 use syntax::ast;
 use syntax::codemap::{Span, COMMAND_LINE_SP};
@@ -100,6 +103,7 @@ impl<'a> PluginLoader<'a> {
     }
 
     // Dynamically link a registrar function into the compiler process.
+    #[allow(deprecated)] // until #23197
     fn dylink_registrar(&mut self,
                         span: Span,
                         path: PathBuf,